The present invention relates to a delay adding device and an ultrasonic diagnostic apparatus, and particularly to a device which delays and adds a plurality of continuous wave signals by an analog delay line having a plurality of taps, and an ultrasonic diagnostic apparatus equipped with such a device.
In an apparatus which performs an ultrasonic diagnosis by a CWD (Continuous Wave Doppler), a continuous ultrasonic sound is transmitted and its echo is received by a plurality of channels. Those received signals are delayed and added by an analog delay line having plural taps to determine a Doppler shift. The delay/addition is performed to adjust or control the orientation of echo reception.
By the use of the fact that the polarity of an input signal is inverted to obtain a delay effect equivalent to one-half wavelength, the analog delay line is scaled down in such a manner that a maximum delay amount reaches less than or equal to one-half wavelength. A plurality of taps are provided on such an analog delay line at delay intervals each corresponding to a ⅛ wavelength or a 1/16 wavelength (refer to, for example, a patent document 1).
[Patent Document 1] Japanese Unexamined Patent Publication No. 2002-291742 (Fifth to sixth pages and FIGS. 1 and 2)